To achieve a high user throughput, coordinated multi-point transmission technology may be used in a communication system.
The coordinated multi-point transmission technology means that multiple access points (Access Point) that are geologically separate provide data transmission services for one or more users at the same time.
For the coordinated multi-point transmission technology, before coordinated multi-point transmission or receiving, selection of the access point/set and scheduling of the time frequency resources used for transmission must be performed. The base station needs to use the channel state information (Channel State Information, CSI) between the terminal and the candidate access point/set as an input or reference to complete the selection of the access point/set and scheduling of the time frequency resources used for transmission.
In a traditional single-point transmission system, the method for downlink channel measurement is as follows: The serving base station transmits the downlink reference signal. The terminal receives the reference signal. The terminal obtains the channel state information through calculation, and then feeds back the channel state information between the terminal and its serving point (single point). For a multi-point transmission system, the preceding operations also need to be performed. The difference is as follows: in multi-point transmission, multiple base stations send downlink reference signals. The terminal needs to receive reference signals from multiple base stations, and feeds back the channel state information between the terminal and multiple serving points. Therefore, for a multi-point communication system, the feedback quantity of the terminal extends from the channel state information between the terminal and a single point to the channel state information between the terminal and multiple points. For a carrier aggregation system, the channel state information on different component carriers needs to be fed back.
In the prior art, for a coordinated multi-point transmission system, the terminal needs to feed back the channel state information between the terminal and all possible serving points or sets; for a carrier aggregation system, the terminal needs to feed back the channel state information between all possible component carriers of the terminal and the serving points. Therefore, in a coordinated multi-point transmission system or a carrier aggregation system, the feedback quantity increases greatly, and occupies huge uplink channel bandwidth, which causes heavy load on the uplink control channel and reduces the spectral efficiency of the entire system.